Infection with human immunodeficiency virus (HIV) has been associated with the development of diverse neurologic complications, yet the full spectrum of neurologic disease remains incompletely characterized. In addition to clinical neurologic detail, unanswered issues include delineation of the incidence, prevalence, and natural history of the neurologic disease, determination of the factors predictive for development of symptomatic neurologic disease, and clinico-pathological correlation. The proposed studies will test three hypotheses. First, neurologic diseases are common in HIV-infected individuals, but their prevalence, manifestations and natural history may vary depending on the route of infection and the presence of other co-factors. Second, specific neurologic syndromes, such as dementia, vacuolar myelopathy, gracile tract degeneration, inflammatory demyelinating polyneuropathy, multiple mononeuropathy, and predominantly sensory neuropathy, occur at specific stages of HIV infection. Third, the types of neuropathies listed above have different pathogeneses. By using a standardized series of neurologic tests in HIV-infected populations with different epidemiologic characteristics, our studies will determine the incidence, prevalence, and natural history of the neurologic disorders associated with HIV infection in both a cross-sectional and longitudinal manner and allow detailed characterization of the different neurologic syndromes. The studies will determine whether clinical and laboratory testing in asymptomatic individuals has predictive value for subsequent neurologic disease, and whether specific determinants of neurologic disease can be identified. In patients with peripheral neuropathy, specific studies utilizing the methods detailed in this and other Sections will be applied to elucidate pathogenesis. These clinical studies will form the basis for close correlation with the immunologic, virologic, and pathologic studies to address issues of pathogenesis.